Heat absorbing glass is used to reduce the amount of heat transmitted through an optical system. SCHOTT KG filter glasses effectively absorb wavelengths beyond the visible spectrum. Unlike hot mirrors, which reflect the infrared wavelengths, KG filter glasses absorb the infrared radiation and then dissipate the heat into the air around the glass. SCHOTT KG filter glasses can also be utilized as a shortpass filter, in order to pass the visible and block the IR. We recommend using a cooling fan with any of our heat absorbing products to reduce stress associated with excessive heat.